The girl's parents had brought her to the hospital to receive treatment for leukemia. The treatment called for a chest catheter to be place into her heart, Phoenix police spokesman Sgt. Steve Martos said.

The girl, identified only as Emily, had to have her arm amputated due to an infection, Martos said.

For unknown reasons, her 35-year-old mother decided to remove the IV from the catheter, changed the child's clothing and walked her out of the hospital, according to Martos.

Surveillance cameras in hallways throughout the hospital recorded their movement to the front doors.

Emily is still in need of immediate medical care. Doctors say if the catheter is not medically removed, the her heart could potentially become infected, resulting in her death, possibly in a matter of days.

Detectives have made every effort to locate Emily and her family to no avail, Martos said.

"It is imperative anyone with information as to the whereabouts of these individuals contact Phoenix police," Martos said. "The primary concern of our detectives is the welfare of the 11-year-old victim."

They left in a black Ford van. No other description of the vehicle is available.

Emily was due to be released from the hospital Thursday morning, Martos said.

Stay with cbs5az.com and CBS 5 News for updates on this developing story.